1. Field of the Invention
The present invention relates to a semiconductor switch such as an RF signal changeover switch or a power resistance switch that mainly operates in a microwave band (300 MHz to 30 GHz) or a millimeter band (30 GHz to 300 GHz), and an MMIC and a module that use the semiconductor switch.
2. Description of the Related Art
In general, a high frequency semiconductor switch is used as a changeover switch of a desired RF signal, such as changeover between transmission and reception, in an RF module that operates in the microwave band or the millimeter band. Further, the high frequency semiconductor switch is used as a power resistance switch for a receiver system for protecting a receiver module, for example, a low-noise amplifier or the like when a signal of high input power is received.
Hereinafter, a conventional semiconductor switch is described with reference to the accompanying drawings.
FIG. 19 is a circuit diagram illustrating a conventional semiconductor switch 50.
Referring to FIG. 19, the semiconductor switch 50 includes a first input/output terminal P1, a second input/output terminal P2, and a third input/output terminal P3. A first field effect transistor (FET) 51 is connected between the first input/output terminal P1 and the second input/output terminal P2. Further, an inductor 52 is connected in parallel between a drain electrode and a source electrode of the first FET 51.
A transmission line 53 having a length of ¼ wavelength with respect to a desired RF signal is connected between the first input/output terminal P1 and the third input/output terminal P3. Further, one of the drain electrode and the source electrode of a second FET 54 is connected between the transmission line 53 and the third input/output terminal P3, and another of the drain electrode and the source electrode is grounded. Further, the gate electrodes of the first FET 51 and the second FET 54 are connected to a control voltage application terminal V1 through gate bias resistors 55 and 56, respectively (for example, refer to JP 2002-164703 A).
FIG. 20 is a circuit diagram illustrating an RF module for a case in which the semiconductor switch 50 illustrated in FIG. 19 is used as a changeover switch.
Referring to FIG. 20, the first input/output terminal P1 of the semiconductor switch 50 is connected to an antenna connection terminal P4. Further, the second input/output terminal P2 is connected to a receiver signal output terminal P5 through a receiver system circuit 57 (low noise amplifier or the like). Further, the third input/output terminal P3 is connected to a transmitter signal input terminal P6 through a transmitter system circuit 58 (amplifier or the like).
In the RF module, at the time of transmission, the semiconductor switch 50 is changed over to connect the first input/output terminal P1 and the third input/output terminal P3, and a transmitter signal input from the transmitter signal input terminal P6 is amplified by the transmitter system circuit 58 and output to the antenna connection terminal P4. On the other hand, at the time of reception, the semiconductor switch 50 is changed over to connect the first input/output terminal P1 and the second input/output terminal P2, and an input signal from the antenna connection terminal P4 is amplified by the receiver system circuit 57 and output to the receiver signal output terminal P5.
FIG. 21 is a circuit diagram illustrating an RF module for a case in which the semiconductor switch 50 illustrated in FIG. 19 is used as a power resistance switch.
Referring to FIG. 21, the first input/output terminal P1 of the semiconductor switch 50 is connected to the antenna connection terminal P4 through a circulator 59. The circulator 59 is connected to the transmitter signal input terminal P6 through the transmitter system circuit 58. The second input/output terminal P2 is connected to the receiver signal output terminal P5 through the receiver system circuit 57. The third input/output terminal P3 is grounded through a resistor 60.
In the RF module, at the time of transmission, the transmitter signal input from the transmitter signal input terminal P6 is amplified by the transmitter system circuit 58, and output to the antenna connection terminal P4 through the circulator 59. On the other hand, at the time of reception, the semiconductor switch 50 is changed over to connect the first input/output terminal P1 and the second input/output terminal P2, and the input signal from the antenna connection terminal P4 is amplified by the receiver system circuit 57 and output to the receiver signal output terminal P5.
In this example, when the input signal received by the antenna connection terminal P4 is of high input power, the semiconductor switch 50 is changed over to connect the first input/output terminal P1 and the third input/output terminal P3, and the input signal is allowed to pass through the resistor 60 serving as a dummy, thereby protecting the receiver system circuit 57.
However, the conventional art suffers from the following problems.
In the conventional semiconductor switch, when the switch is used as a power resistance switch of the RF module, it is necessary to detect a power level of the input signal at the time of reception and change over the semiconductor switch according to the power level. For that reason, it is necessary to provide a detector circuit for detecting the power level at the input side of the receiver system, which leads to such a problem that the performance is deteriorated with an increase in the loss of the receiver system.
Further, in addition to the above-mentioned detector circuit, a control circuit that controls the switching operation of the semiconductor switch is also required, resulting in such a problem that the circuit configuration is upsized.
Further, as another method, it is conceivable to provide a limiter or the like that reduces an excessive input power down to a constant level, at an input side of the receiver system. However, in this case, similarly, there arises such a problem that the performance is deteriorated with an increase in the loss of the receiver system.